Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates. This week’s article was written by research geophysicist Jim Kauahikaua.

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Two projects that will start this summer employ flying an oblong wire loop and burying wire coils.  The target area is the entire volcano of Kīlauea—from the eastern point of Kumukahi southwest almost to Punaluʻu. Warning: many acronyms to follow! Both projects will determine the distribution of electrical resistivities below the surface that can be used to map magma and hot rock, among other things. The airborne project will also map variations in the magnetic field to determine how well the Earth's field is frozen into Kīlauea's magnetic minerals.

The first project will deploy electrodes and wire coils buried at shallow depths to passively measure the electromagnetic (EM) energy generated by lightning strikes around the equator. The technique is called magnetotelluric (MT) sounding. Lightning storms are common in equatorial regions and those storms produce surprisingly constant electromagnetic noise that travels around the globe in the atmosphere between the Earth's surface and the ionosphere.

The response of the earth to this distant EM stimulation can tell us the electrical properties of the earth below the coils to depths of about 10 km (6 mi). The one-square-meter (yard) setup will be moved to about 125 ground locations on the volcano. The resulting data will be used to develop a detailed picture of Kīlauea's inner workings. This study will be done over two field seasons with the first season in 2022 during the months of May and June. The second season will be in the summer of 2023.

The second part of this project will use a 15 by 25 m (50 by 80 ft) oval-shaped wire loop suspended 30 m (100 ft) beneath a helicopter (Fig. 1) flying over most of the volcano. The loop assembly will transmit and receive very, very low frequency EM energy and will need to be flown 35–50 m (115–165 ft) above the ground or treetops. A small sensor will also be measuring magnetic field strength. The technique is called airborne electromagnetic and magnetic (AEM) mapping.

AEM data will complement the MT data and allow imaging of the shallow (upper 600 m or 2,000 ft) structure of the volcano including groundwater and patterns of alteration caused by hydrothermal fluids like those that seeped into Halemaʻumaʻu water lake in 2019–2020. Earth's magnetic field along the flight path will also map the signature of the cooling dike that transported magma to lower Puna in 2018. This part of the project is also scheduled for 2022 in the months of June and July.

Currently planned flight lines do not fly over any residential areas or other regions excluded by the Federal Aviation Administration (FAA) or Hawaiʻi Volcanoes National Park (HVNP). Flights will occur during daylight hours and be coordinated with the FAA. Experienced pilots specially trained and approved for low-level flying will operate the helicopter. None of the instruments in either part of the project pose a health risk to people or animals.

AEM and Earth's magnetic field were last mapped in 1978 over both Kīlauea and Mauna Loa volcanoes. The 1978 results showed that Kīlauea's East Rift Zone was clearly outlined by a strong magnetic field aberration typical of vertical dikes that fed countless eruptions laterally from the summit area.

The equipment and software have been much improved in the past 20 years and the geophysicists overseeing the current project have successfully used the technique to map other US volcanoes. Our hopes are high that we will be able to more clearly image to greater depths in this new project to produce a picture of the entire magmatic system of Kīlauea. The final products of this survey will be made public within a few years.

The AEM survey should take about three weeks starting in late June. We understand that helicopter noise can be disruptive, so we will greatly appreciate affected residents' patience and understanding as we collect this extremely important data to help mitigate future eruption hazards.

Volcano Activity Updates

Kīlauea volcano is erupting. Its USGS Volcano Alert level is at WATCH (https://www.usgs.gov/natural-hazards/volcano-hazards/about-alert-levels). Kīlauea updates are issued daily.    

Over the past week, lava has continued to erupt from the western vent within Halemaʻumaʻu crater. All lava is confined within Halemaʻumaʻu crater in Hawai‘i Volcanoes National Park. Sulfur dioxide emission rates remain elevated and were last measured at approximately 2,300 tonnes per day (t/d) on May 22. Seismicity is elevated but stable, with few earthquakes and ongoing volcanic tremor. Summit tiltmeters showed two deflation-inflation cycles over the past week. For more information on the current eruption of Kīlauea, see https://www.usgs.gov/volcanoes/kilauea/recent-eruption.

Mauna Loa is not erupting and remains at Volcano Alert Level ADVISORY. This alert level does not mean that an eruption is imminent or that progression to an eruption from the current level of unrest is certain. Mauna Loa updates are issued weekly.     

This past week, about 50 small-magnitude earthquakes were recorded below the summit and upper elevation flanks of Mauna Loa—the majority of these occurred at shallow depths less than 15 kilometers (9 miles) below sea level. Global Positioning System (GPS) measurements show low rates of ground deformation over the past week. Gas concentrations and fumarole temperatures at both the summit and at Sulphur Cone on the Southwest Rift Zone have remained stable over the past week. Webcams show no changes to the landscape. For more information on current monitoring of Mauna Loa, see: https://www.usgs.gov/volcanoes/mauna-loa/monitoring.  

One earthquake was reported felt in the Hawaiian Islands during the past week: a M4.7 earthquake 3 km (1 mi) NW of Hōlualoa at 9 km (5 mi) depth on May 21 at 11:49 p.m. HST.

HVO continues to closely monitor Kīlauea's ongoing eruption and Mauna Loa for any signs of increased activity.    

Please visit HVO’s website for past Volcano Watch articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake info, and more. Email questions to askHVO@usgs.gov.    

Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.